It is common for engine controllers to provide control based on engine crankshaft angular position. For example, in combustion timing control, the timing involves either the crankshaft angle location of spark for gas fueled engines or the crankshaft angle of fuel injection for diesel fueled engines. In each of these engines, the crankshaft timing angles are generally referenced to the engine piston top dead center positions.
Two sensors are typically used to establish the desired crankshaft angles. One sensor provides crankshaft position signals at the piston top dead center positions of each cylinder. In a diesel engine, this sensor may take the form of a one-tooth per cylinder gear and a tooth sensor mounted in the engine driven solenoid pump. This sensor provides an indication of the location of the top dead center position for each cylinder and is the basis for engine timing. Signal resolution for an 8-cylinder engine is one pulse per 90 degrees.
The second sensor generates angle signals at small increments of engine crankshaft rotation. Typically, these angle pulses are obtained by monitoring the passing of the teeth on the engine ring gear by an electromagnetic pickup. These teeth are spaced at two to three degree intervals around the ring gear so that an electrical pulse is provided for each two to three degrees of angular rotation of the engine. These crankshaft angle signals in conjunction with the crankshaft position signal provided at each piston top dead center position of the engine enable the location of desired crankshaft angles for fuel control and combustion timing.
In the foregoing systems, if there is a failure in the sensor providing the crankshaft angle signals, the system would be incapable of providing accurate control of fuel or combustion timing to the engine. For example, if one of the teeth spaced around the flywheel for providing the crankshaft angle signals should wear or break off resulting in a loss of the corresponding crankshaft angle signal, a deterioration in the control of fuel and combustion timing would result.